Apparatus for reconstructing speech generated in an abnormal gas atmosphere

ABSTRACT

The reconstruction of distorted speech due to an abnormal breathing atmosphere is accomplished by providing a series of separate channels each supplied with a white noise signal and having therein a narrow band filter and an amplitude controllable amplifier. The control input of each amplifier is connected to a microphone disposed within a Helmholtz resonator whose resonant frequency in air is equal to that of the filter associated with that particular amplifier. The resonators are disposed in an atmosphere identical to that of the person whose speech is to be reconstructed or proximate the speaker and are subjected to the distorted acoustic speech. The outputs of the amplifiers are simultaneously applied to an output amplifier which in turn drives a transducer such as a loudspeaker to provide a corrected speech pattern.

United States Patent [72] Inventor Willard D. Carpenter San Diego,Calif.

[21 Appl. No. 17,407 [22] Filed Mar. 9, 1970 [45] Patented Aug. 17, 1971[73] Assignee The United States of America as represented by theSecretary of the Navy [54] APPARATUS FOR RECONSTRUCTING SPEECH GENERATEDIN AN ABNORMAL GAS ATMOSPHERE 6 Claims, 2 Drawing Figs.

[52] US. Cl 179/1 SA [51] 1nt.C! G101 l/00 [50] Field of Search 179/1SA;

[5 6] References Cited UNITED STATES PATENTS 3,165,734 4/1965 Grodzinsky340/384 E 3,270,833 9/1966 Schroeder .4 179]] SA 3,394,228 7/1968Flanagan Primary ExaminerKathleen H. Claffy Assistant Examiner-JonBradford Leaheey Attorneys-Richard S. Sciascia, Louis B. Applebaum andErnest F. Weinberger that of the filter associated with that particularamplifier. The

resonators are disposed in an atmosphere identical to that of the personwhose speech is to be reconstructed or proximate the speaker and aresubjected to the distorted acoustic speech. The outputs of theamplifiers are simultaneously applied to an output amplifier which inturn drives a transducer such as a loudspeaker to provide a correctedspeech pattern.

APPARATUS FOR RECONSTRUCTING SPEECH GENERATED IN AN ABNORMAL GASATMOSPHERE The invention described herein may be manufactured and usedby or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to speech reconstruction and more particularlypertains to the correction or synthesis of voice distortion resultingfrom speaking in an abnormal gaseous environment.

' 2. Description of the Prior Art In the field of voice reconstruction,it has been thegeneral practice to employ complex electronic equipmentwherein the acoustic voice signal is first converted into its electricalanalog which is then processed by frequency separation. Each separatefrequency channel is independently shifted by a specific amount and thechannel outputs reassembled to provide the undistorted speech pattern.Such devices have been unsatisfactory in that, where attempts have beenmade to employ them for correcting speech distorted by an abnormalgaseous environment, either prior complex calculations or trial anderror methods are necessary to determine proper processing values foreach channel.

SUMMARY OF THE INVENTION The general purpose of this invention is toprovide a voice distortion correction apparatus that has all theadvantages of similarly employed prior art devices and has none of theabove-described disadvantages. To attain this, the present inventionprovides a unique speech reconstruction system wherein a microphonedisposed within the chamber of a Helmholtzjresonator, tuned to aspecific frequency, controls the amplitude of an amplifier which isreceiving white noise in the same frequency spectrum. A plurality ofchannels are employed to cover the voice spectrum and their outputscombined to provide undistorted speech. The Helmholtz resonators arelocated in the environment of the speaker or in an identical gaseousenvironment whereby automatic frequency shifting is attained.

An object of the present invention is to provide a simple, direct,inexpensive and reliable apparatus for correcting distorted speechinduced by the speakers presence in an abnormal gaseous environment. I

Another object is to provide an'apparatus for automatic reconstructionof speech having been distorted so as to be unintelligible by anabnormal gaseous atmosphere and to improve intelligibility.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description whenconside redinconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE'DRAWINGS FIG. 1 is a schematic diagram of anembodiment made in accordance with the principle of this invention; and

FIG. 2 illustrates a modification-of the embodiment of FIG.

1 wherein sensing transducers are located proximate the speakers face.

DESCRIPTIONOF THEPREFERREDEMBODIMENTS teristics of the voice throughpositioning of the tongue, palate,

cheeks, lips and teeth. The use and dexterity of the muscles to shapesounds and to form them into words is learned early in life andthereafter becomes an automatic process necessitating little or noconscious effort. It is clear, however, that the use of these resonantcavities to form intelligible speech is adapted to an air environment.When a speaker attempts to talk in other than normal air" atmosphere, hemakes use of his muscles to shape the resonant cavities that wouldproduce normal speech in-air. Since the characteristic frequency of aresonant cavity depends not only on the physical dimensions of thecavity but also on the velocity of the acoustic wave in the medium whichfills the cavity, the resultant voice sounds unnatural. v t

The velocity of sound in an atmosphere is a functionof the particulargas which comprises the atmosphere, its-temperature and pressure. Theeffect or correction for pressure is relatively negligible, while thevelocity is approximately proportional to the square root of theabsolute temperature. This also has very little effect on any frequencyshift. The factor most responsible for changes in voice characteristics,resulting in distorted speech, is the gas chosen as the breathingmixture. In deep diving operations, a helium-oxygen mixture is mostoften employed. The speed of sound in pure helium at 0 C. at latmosphere pressure, is 3,182 ft./sec., compared to 1,087.5 ft./sec. forair under identical conditions. Since the characteristic acousticresonance of a cavity is directly proportional to, the speed of sound,the replacement of the normal atmosphere by a helium-oxygen breathingmixture causes the voice formants to shift upward in frequency. Thisupward shift is accomplished by a spreading in the formants caused byeach resonant frequency shifting by a different amount.

As an example, consider a typical voice formant which encompasses afrequency range of 300 to 1,000 Hertz in a normal atmosphere. Thesubstitution of a new breathing mixture which caused the acousticvelocity to double would result in the formant shifting to cover thefrequency range of 600 to 2,000 Hertz. This fact has been confirmed byvoice prints made in both normal and helium-oxygen atmospheres.

In view ofthe foregoing, in order to restore the distortion caused by anew breathing mixture, it would be necessary to shift down and compressthe formants by an amount equal to the up shift and spreading due to themixture. An apparatus to accomplish this is illustrated in FIG. 1, wherea plurality of channels l0-l8'are connected to each receive the outputof a white or random noise source 19. Each channel has connectedthereinin series or tandem a narrow band filter 20-28 and an amplitudeor gain controllable amplifier 29-37. The filters preferably are of theelectrical type, and each covers a differentnarrow band of the voiceintelligence spectrum, so that in total they cover the entire spectrum,or at least those bands contributing to overall intelligence. One suchspectrum of voice formants would be 300 to 1,000 Hertz where, forexample, the first filter 20 in channel 10 would cover the narrow rangeof 300 to 350 Hertzand the last filter 28 would cover 902-'-l,000 Hertz.Each of these amplifiers (29-37) is provided with an input terminal I,an output terminal Oand intermediate thereof a control input C whichcontrols the gain or output amplitude of its amplifier dependenton thevoltage ap plied. The amplifier outputs O are all joined to a commonoutput 38 and feed a broadband output amplifier 39, which in turn drivesa transducer or loudspeaker 40.

Each of the control terminals C is directlytied to a sound pressuresensing transducer such as microphones 41-49 which is relativelyomnidirectional and broadband. The microphones are each located withinthe cavity of a Helmholtz resonator 50--58. (Essentially, a Helmholtzresonator is a cavity provided with a small aperture. The ratio of theenclosed volume tothe aperture diameter (or area) determines thefrequency resonance thereof. Since the ratio of the acoustic pressuredeveloped inside the resonator to that of free space varies inverselywith the volume of the resonator cavity, byproviding a small volume, theresonatorwillexhibit a sharp pressure peak over a narrow frequency band.Thus eachresonator can be made resonant in air over the narrow band-passof the respective filter with which its associate.

The Helmholtz resonators 50-58 and the microphones 41'49 are alldisposed and supported within a gas sealed tank or chamber 59, which isprovided with an inlet port 60 and an outlet port 61. This chamber, forbest results, should be acoustically deadened.

Where this apparatus is to be employed with a deep driving hard-hatdiver using ahelium-oxygen mixture, or some other than air breathingmixture, helmet 62 isconnected by hose 63 to the chamber 59, outlet port61, while inlet port 60 is connected to the source of breathing mixture64 via hose 65. This insures that the Helmholtz resonators will beexposed to a gaseous environment identical to that of the diver and oneinto which he speaks. Microphone 66 in helmet 62 is electricallyconnected toa loudspeaker 67 disposed in the chamber opposite theresonators via cable 68 and, where necessary, broadband amplifier 69.With this arrangement the divers voice, which is distorted, isreproduced withing the chamber. Since the effect of an other than normalatmosphere is minimal for a loudspeaker, no additional voice distortionis introduced by the loudspeaker 67. 7

Consider now the embodiment of FIG. 2. Here, the divers helmet 70 isprovided with a plurality of Helmholtz resonators 50'--58' supported onthe inner wall of the helmetopposite or proximate the mouth of thediver. The breathing mixture is supplied to the helmet by hose 63' fromthe source, which is generally located on the ship. The microphones4l-49 are located within the cavities of the resonators and connected bymultiple wire cable 72 to their respective controllable ammicrophone isplifiers onthe ship. This arrangement obviates the necessity ofemploying a separate chamber aboard the ship and an additionalmicrophone and loudspeaker to reproduce the divers voice therein.

Summarizing the operation a series of Helmholtz resonators are placedinto an acoustically deadened chamber. The divers speech is supplied tothe chamber and the divers breathing mixture comprises the atmosphere ofthe chamber. A microphone is placed into the Helmholtz resonator tomeasure the sound pressure developed in the cavity.

By inserting a microphone into the cavity and placing the Helmholtzresonator into an acoustic field, the output of the microphone will giveus an output which varies directly with the amplitude of the narrow bandof frequencies at which the cavity is resonant. This output can be usedto control the gain of an amplifier.

The input of the amplifier is a narrow band of frequencies which is thenarrow band at which the Helmholtz resonator is resonant in air. As theHelmholtz resonator responds to an acoustic field in air, it willcontrol the gain of an amplifier supplying the same narrow band offrequencies to a loudspeaker.

By using a series of resonators throughout the audio spectrum to controlamplifiers whose inputs correspond to the frequencies of the resonatorsin air the output at the loudspeaker will correspond to the acousticalinput in air.

The inputs to the controlled amplifiers can be obtained by a series ofnarrow band filters at the output of a white noise source. The output ofeach narrow band filter will supply the input to a controlled amplifier.A Helmholtz resonator microphone combination will supply the controlsignal. The output of each controlled amplifier will always be the samenarrow band of frequencies, and it will be the narrow band offrequencies at which the Helmholtz resonator which supplies itscontrolling signal is resonant in air.

When the atmosphere in the chamber which contains the series ofHelmholtz resonators is changed to. a different gas the narrow frequencyband at "which.- the Helmholtz cavity mosphere in the'chamber isthesame-as what is breathed by the speaker, the system will compensate theshift and spread of the voice characteristics and provide an outputsimilar-to the voice characteristics of the speaker in air.

For example, taking a typical voice formant of 300 to 1,000 Hertz inair, we know that if; the. speakers breathing atmosphere were changed to"one in which the speed of sound doubled the formant would now occupy600 to 2,000 Hertz. If we introduce the new atmosphere to the chambercontaining the series of Helmholtzresonators, the resonators coveringthe spectrum of 300 to 1,000-Hertz in air will cover the spectrum 600 to1,000 Hertz in the new atmosphere. However, these resonators will supplycontrolling signals to amplifiers whose output covers the 300 to 1,000Hertz spectrum.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

I claim:

1. An apparatus for correcting the acoustic distortion of the reproducedvoice of a diver breathing an other than normal atmosphere whichcomprises;

a plurality of audio channels each having connected, in tandem therein,a narrow band filter, a gain controllable amplifier having input andoutput terminals and acontrol terminal, v v

said channels each having its filter .tuned to a different centerfrequency to cover a portion of the audio spectrum,

a source of random noise having its output connected simultaneously toeach of said filters,

a closed chamber having therein an atmosphere identical to that of saiddiver and having disposed therein a plurality of Helmholtz resonatorseach tuned in air frequency identical to one of said filters,

an acoustic transducer for each of said resonators disposed to sense theacoustic pressure in each of said resonators, mean connecting each ofsaid transducers with said control terminal of said gain controllableamplifier which is in tandem with said filter tuned to the samefrequency as said resonator associated with that transducer, acousticoutput means connected simultaneously to said output of said amplifiers,and I reproducing means disposed in said chamber and connected toreproduce the distorted speech of said diver therein, whereby the outputfrom said acoustic means will convert said divers voice intointelligible speech.

2. The apparatus according to claim 1 wherein said transducers aremicrophones.

3. The apparatus according to claim 2 wherein said acoustic output meansis a loudspeaker.

4. The apparatus according to claim 3 wherein said reproducing means isin part, external to said chamber and includes: I

a speaker's microphone disposed proximate said divers face, a secondloudspeaker disposed within said chamber, and

an electrical connection between said second loudspeaker and saidspeaker's microphone.

5. An apparatus for correcting the acoustic distortion of a diver usinga diving helmet and breathing an other than normal atmosphere, whichcomprises:

a plurality of audio channels each having connected in tandem therein: 7I

a narrow band filter, Y

a gain controllable amplifier having input and output terminals and acontrol terminal,

said channels each having its filter tuned to a difi'erent centerfrequency to "coverta portion of the audio spectrum, I

' a source of random noise having its output connected simultaneouslytoeach of said filters said helmet having disposed therein;

a plurality of Helmholtz resonators each tuned in air to a frequency.identicalto one of said filters,

to a

acoustic output means connected simultaneously to said output of saidamplifiers, I 6. The apparatus according to claim 5 wherein saidtransducers are microphone and said acoustic output means is aloudspeaker.

1. An apparatus for correcting the acoustic distortion of the reproducedvoice of a diver breathing an other than normal atmosphere whichcomprises; a plurality of audio channels each having connected, intandem therein, a narrow band filter, a gain controllable amplifierhaving input and output terminals and a control terminal, said channelseach having its filter tuned to a different center frequency to cover aportion of the audio spectrum, a source of random noise having itsoutput connected simultaneously to each of said filters, a closedchamber having therein an atmosphere identical to that of said diver andhaving disposed therein a plurality of Helmholtz resonators each tunedin air to a frequency identical to one of said filters, an acoustictransducer for each of said resonators disposed to sense the acousticpressure in each of said resonators, mean connecting each of saidtransducers with said control terminal of said gain controllableamplifier which is in tandem with said filter tuned to the samefrequency as said resonator associated with that transducer, acousticoutput means connected simultaneously to said output of said amplifiers,and reproducing means disposed in said chamber and connected toreproduce the distorted speech of said diver therein, whereby the outputfrom said acoustic means will converT said diver''s voice intointelligible speech.
 2. The apparatus according to claim 1 wherein saidtransducers are microphones.
 3. The apparatus according to claim 2wherein said acoustic output means is a loudspeaker.
 4. The apparatusaccording to claim 3 wherein said reproducing means is in part, externalto said chamber and includes: a speaker''s microphone disposed proximatesaid diver''s face, a second loudspeaker disposed within said chamber,and an electrical connection between said second loudspeaker and saidspeaker''s microphone.
 5. An apparatus for correcting the acousticdistortion of a diver using a diving helmet and breathing an other thannormal atmosphere, which comprises: a plurality of audio channels eachhaving connected in tandem therein: a narrow band filter, a gaincontrollable amplifier having input and output terminals and a controlterminal, said channels each having its filter tuned to a differentcenter frequency to cover a portion of the audio spectrum, a source ofrandom noise having its output connected simultaneously to each of saidfilters said helmet having disposed therein; a plurality of Helmholtzresonators each tuned in air to a frequency identical to one of saidfilters, an acoustic transducer for each of said resonators disposed tosense the acoustic pressure in each of said resonators, means connectingeach of said transducers with said control terminal of said gaincontrollable amplifier which is in tandem with said filter tuned to thesame frequency as said resonator associated with that transducer, andacoustic output means connected simultaneously to said output of saidamplifiers,
 6. The apparatus according to claim 5 wherein saidtransducers are microphone and said acoustic output means is aloudspeaker.